1. Field of the Invention
The invention relates to an adjustable connecting device for interconnecting seat and backrest members of a chair, more particularly to a concealable height adjustable device adapted to adjust the height of the backrest member relative to the seat member.
2. Description of the Related Art
FIG. 1 shows a conventional backrest-height adjustable chair 1. The chair 1 includes a seat member 11, a backrest member 12, an upright post 13 disposed at a bottom side of the seat member 11, and a connecting device 2 for interconnecting the seat and backrest members 11, 12. The backrest member 12 includes front and rear backrest portions 121, 122. With reference to FIG. 2, the connecting device 2 includes a casing 21 and a generally L-shaped mounting frame 22 having an upper end portion inserted into the casing 21. The casing 21 and the mounting frame 22 are capable of sliding displacement relative to each other. The casing 21 is provided with a retaining key 211 that can be manipulated to slide along a keyway 221 in the upper end portion of the mounting frame 22 to engage one of a plurality of notches 222 communicated with the keyway 221 so as to position the backrest member 12 at a desired level. During assembly, the casing 21 together with the upper end portion of the mounting frame 22 retained therein has to be first secured to the rear side of the front backrest portion 121 or the front side of the rear backrest portion 122 at four corner portions 223 thereof via screws 224 before the front and rear backrest portions 121, 122 can be coupled. Then, a lower end portion of the mounting frame 22 is secured to the seat member 11.
Since the casing 21 together with the upper end portion of the mounting frame 22 have to be secured firmly to the front or rear backrest portion 121, 122 before the front and rear backrest portions 121, 122 are coupled, the connecting device 2 is usually connected to the backrest member 2 in the factory before delivery to retailers, where the backrest member 12 is connected to the seat member 11. As the L-shaped mounting frame 22 projects from the backrest member 12 to quite a distance, a large amount of packaging material is needed. Besides, if the height of the backrest member 12 relative to the seat member 11 has to be further adjusted, the front and rear backrest portions 121, 122 have to be taken apart.